1. Field of the Invention
The present invention relates to a regenerative pump.
2. Description of Related Art
The regenerative pump is a pump, in which a plurality of blades is driven in an annular fluid passage to provide kinetic energy to a fluid supplied into the fluid passage. The regenerative pump is used to, for example, supply air to exhaust gas discharged from an internal combustion engine to reduce emissions contained in the exhaust gas.
One type of regenerative pump is recited in, for example, Japanese Unexamined Patent Publication No. 7-119686 or FIG. 8. This type of regenerative pump will be described with reference to FIG. 8. In FIG. 8, a blade passing zone cross sectional area of a fluid passage of the regenerative pump 100 has a semi-round shape, and a blade non-passing zone cross sectional area of the fluid passage also has a semi-round shape. Here, the blade passing zone cross sectional area is defined as a portion of a cross section of the fluid passage, through which the blades 101 pass through. Here, the cross section of the fluid passage is perpendicular to a flow direction of a mainstream of the fluid in the fluid passage. Furthermore, the blade non-passing zone cross sectional area is defined as a portion of the cross section of the fluid passage, through which the blades 101 do not pass. Another type of regenerative pump is recited in, for example, Japanese Unexamined Patent Publication No. 7-119686 or FIG. 9. This type of regenerative pump will be described with reference to FIG. 9. In FIG. 9, the blade passing zone cross sectional area of the regenerative pump 100 has a generally quarter-round shape, and the blade non-passing zone cross sectional area of the regenerative pump 100 has a shape that includes a semi-round portion and a linear portion. The linear portion extends from one end of the semi-round portion.
With reference to FIGS. 10 and 11, which show partial enlarged views of FIGS. 8 and 9, respectively, the fluid supplied into the regenerative pump 100 receives kinetic energy from the blades 101. Thus, the fluid sequentially moves from one to the next recess, each of which is defined between corresponding adjacent blades 101, while the fluid swirls between a blade passing zone and a blade non-passing zone. Here, the blade passing zone is defined as a portion of the fluid passage, through which the blades 101 pass. Also, the blade non-passing zone is defined as a portion of the fluid passage, through which the blades 101 do not pass.
The flow of the refrigerant, which swirls between the blade passing zone and the blade non-passing zone, will be hereinafter referred to as a swirl flow. The flow rate of the swirl flow is relatively high in the blade passing zone and also in an outer peripheral part of the blade non-passing zone. However, the flow rate of the swirl flow is slowed down toward the center of the blade non-passing zone and becomes substantially zero at or around the center of the blade non-passing zone. Thus, as in the case of the swirl flow of the regenerative pump 100 shown in FIG. 10 or 11, when the center of the swirl flow is displaced away from an axial side outer edge of the blade 101 (a left side edge of the blade 101 in FIG. 10 or 11) into the blade non-passing zone, the blade non-passing zone has a non-returning region, from which the fluid does not return to the blade passing zone. Here, the axial side outer edge of the blade 101 is defined as an outer edge of the blade 101, which is located in one end of the blade 101 (a left end of the blade 101 in FIG. 10 or 11) in a direction parallel to a rotational axis of the blades 101. The fluid placed in the non-returning region cannot receive the kinetic energy from the blades 101, so that the flow rate of the mainstream of the fluid decreases. As a result, a discharge rate of the regenerative pump 100 decreases, and thereby a pump efficiency of the regenerative pump 100 decreases.
Even when the center of the swirl flow is shifted toward the axial side outer edge of the blade 101 to reduce a size of the non-returning region, the pump efficiency of the regenerative pump 100 may be reduced due to an inappropriate ratio between the blade non-passing zone cross sectional area and the blade passing zone cross sectional area.
For example, when the blade non-passing zone cross sectional area is too small relative to the blade passing zone cross sectional area, an area, through which the fluid can move in the flow direction of the mainstream of the fluid, becomes small. Thus, the flow rate of the fluid in the flow direction of the mainstream becomes too large. As a result, friction loss caused by a wall of the fluid passage becomes large, and thereby the pump efficiency of the regenerative pump 100 is reduced. This is typical in a case where the fluid is discharged from the regenerative pump 100 at the low pressure.
In contrast, when the blade non-passing zone cross sectional area is too large relative to the blade passing zone cross sectional area, a non-swirl area, in which the substantial swirl flow does not exist, will be generated at a radial inner wall of the fluid passage, as shown in FIG. 7. The fluid in the non-swirl area cannot receive the kinetic energy from the blades 101. Thus, the flow rate in the flow direction of the mainstream is reduced. In this way, the discharge rate of the regenerative pump 100 is reduced, and thereby the pump efficiency of the regenerative pump 100 is reduced. This is typical in a case where the fluid is discharged from the regenerative pump 100 at the high pressure.